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      1 This folder is a subpackage of ttLib. Each module here is a 
      2 specialized TT/OT table converter: they can convert raw data 
      3 to Python objects and vice versa. Usually you don't need to 
      4 use the modules directly: they are imported and used 
      5 automatically when needed by ttLib.
      6 
      7 If you are writing you own table converter the following is 
      8 important.
      9 
     10 The modules here have pretty strange names: this is due to the 
     11 fact that we need to map TT table tags (which are case sensitive) 
     12 to filenames (which on Mac and Win aren't case sensitive) as well 
     13 as to Python identifiers. The latter means it can only contain 
     14 [A-Za-z0-9_] and cannot start with a number. 
     15 
     16 ttLib provides functions to expand a tag into the format used here:
     17 
     18 >>> from fontTools import ttLib
     19 >>> ttLib.tagToIdentifier("FOO ")
     20 'F_O_O_'
     21 >>> ttLib.tagToIdentifier("cvt ")
     22 '_c_v_t'
     23 >>> ttLib.tagToIdentifier("OS/2")
     24 'O_S_2f_2'
     25 >>> ttLib.tagToIdentifier("glyf")
     26 '_g_l_y_f'
     27 >>> 
     28 
     29 And vice versa:
     30 
     31 >>> ttLib.identifierToTag("F_O_O_")
     32 'FOO '
     33 >>> ttLib.identifierToTag("_c_v_t")
     34 'cvt '
     35 >>> ttLib.identifierToTag("O_S_2f_2")
     36 'OS/2'
     37 >>> ttLib.identifierToTag("_g_l_y_f")
     38 'glyf'
     39 >>> 
     40 
     41 Eg. the 'glyf' table converter lives in a Python file called:
     42 
     43 	_g_l_y_f.py
     44 
     45 The converter itself is a class, named "table_" + expandedtag. Eg:
     46 
     47 	class table__g_l_y_f:
     48 		etc.
     49 
     50 Note that if you _do_ need to use such modules or classes manually, 
     51 there are two convenient API functions that let you find them by tag:
     52 
     53 >>> ttLib.getTableModule('glyf')
     54 <module 'ttLib.tables._g_l_y_f'>
     55 >>> ttLib.getTableClass('glyf')
     56 <class ttLib.tables._g_l_y_f.table__g_l_y_f at 645f400>
     57 >>> 
     58 
     59 You must subclass from DefaultTable.DefaultTable. It provides some default
     60 behavior, as well as a constructor method (__init__) that you don't need to 
     61 override.
     62 
     63 Your converter should minimally provide two methods:
     64 
     65 class table_F_O_O_(DefaultTable.DefaultTable): # converter for table 'FOO '
     66 	
     67 	def decompile(self, data, ttFont):
     68 		# 'data' is the raw table data. Unpack it into a
     69 		# Python data structure.
     70 		# 'ttFont' is a ttLib.TTfile instance, enabling you to
     71 		# refer to other tables. Do ***not*** keep a reference to
     72 		# it: it will cause a circular reference (ttFont saves 
     73 		# a reference to us), and that means we'll be leaking 
     74 		# memory. If you need to use it in other methods, just 
     75 		# pass it around as a method argument.
     76 	
     77 	def compile(self, ttFont):
     78 		# Return the raw data, as converted from the Python
     79 		# data structure. 
     80 		# Again, 'ttFont' is there so you can access other tables.
     81 		# Same warning applies.
     82 
     83 If you want to support TTX import/export as well, you need to provide two
     84 additional methods:
     85 
     86 	def toXML(self, writer, ttFont):
     87 		# XXX
     88 	
     89 	def fromXML(self, (name, attrs, content), ttFont):
     90 		# XXX
     91 
     92